Americans nearly universally speed, and excess speed is a factor in many accidents. But what if higher speed limits made roads safer?
The answer lies in realizing that the speed limit really is just a number on a sign, and it has very little influence on how fast people drive.
a minority of drivers do follow the speed limit. … This is important because, as noted in a U.S. Department of Transportation report, “the potential for being involved in an accident is highest when traveling at speed much lower or much higher than the majority of motorists.” … Traffic engineers believe that the 85th percentile speed is the ideal speed limit because it leads to the least variability between driving speeds and therefore safer roads.
In its 1992 report, the U.S. Department of Transportation cautioned, “Arbitrary, unrealistic and nonuniform speed limits have created a socially acceptable disregard for speed limits.”
Source: Is Every Speed Limit Too Low?